In a large skillet, melt the butter over medium heat. Add the onions, celery and celery leaves. Cook, stirring often, until the onions are golden, about 8 minutes. Scrape the vegetables and butter into a large bowl. Mix in the bread cubes, parsley, poultry seasoning, salt and pepper. Gradually stir in about 1 1/2 cups of the broth, until the stuffing is evenly moistened but not soggy. Use as a stuffing or place in a lightly buttered casserole and drizzle with 1/2 cup of the broth, cover and bake for 30 to 40 minutes.